The present invention relates to an optical storage medium having two or more of recording layers.
Optical storage media, such as DVDs, having two recording layers have been developed to meet the demands of recording/reproduction of a large amount of data.
Japanese Patent Un-examined Publication No. 2001-266402 discloses an optical storage medium having two composite layers. One composite layer has a first recording layer formed on a first substrate. The other composite layer has a second recording layer formed on a second substrate. The layers are bonded to each other so that the substrates are provided outside. In reproduction, a laser beam is incident through the first substrate and focused onto the first or the second recording layer to reproduce data therefrom. This type of optical storage media having two recording layers, illuminated with a laser beam on one side in reproduction, is called a single-sided dual-layer optical storage medium, hereinafter.
Also heavily developed is a single-sided dual-layer optical storage medium of write-once type having two recording layers made with an organic dye, protected from overwriting once data being written.
There are several schemes to reduce jitters or lower error rates in a write-once type optical storage medium having a single recording layer made with an organic dye. For, example, Japanese Patent Un-examined Publication No. 2002-254822 discloses a specific solvent that dissolves an organic dye. Japanese Patent Un-examined Publication No. 2001-26180 discloses formation of recording layers with several type of dyes exhibiting different maximum absorption wavelengths (λmax).
The above two schemes are effective for a single-layer write-once type optical storage medium, not for a single-sided dual-layer optical storage medium of write-once type, discussed above.